Problem: Solve for $x$ and $y$ using substitution. ${-x-3y = -4}$ ${x = -2y+3}$
Explanation: Since $x$ has already been solved for, substitute $-2y+3$ for $x$ in the first equation. ${-}{(-2y+3)}{- 3y = -4}$ Simplify and solve for $y$ $2y-3 - 3y = -4$ $-y-3 = -4$ $-y-3{+3} = -4{+3}$ $-y = -1$ $\dfrac{-y}{{-1}} = \dfrac{-1}{{-1}}$ ${y = 1}$ Now that you know ${y = 1}$ , plug it back into $\thinspace {x = -2y+3}\thinspace$ to find $x$ ${x = -2}{(1)}{ + 3}$ $x = -2 + 3$ ${x = 1}$ You can also plug ${y = 1}$ into $\thinspace {-x-3y = -4}\thinspace$ and get the same answer for $x$ : ${-x - 3}{(1)}{= -4}$ ${x = 1}$